Use String.to_char_list when converting shell commands

We have found this bug as rebar failed to compile projects
with non-latin characters on the path. Using String.to_char_list
performs the proper conversion, passing the proper arguments
to rebar.

lib/mix/lib/mix/shell.ex

@@ -111,11 +111,11 @@ defmodule Mix.Shell do
       {:unix, _} ->
         command = command
           |> String.replace("\"", "\\\"")
-          |> :binary.bin_to_list
+          |> String.to_char_list
         'sh -c "' ++ command ++ '"'
 
       {:win32, osname} ->
-        command = :binary.bin_to_list(command)
+        command = String.to_char_list(command)
         case {System.get_env("COMSPEC"), osname} do
           {nil, :windows} -> 'command.com /c ' ++ command
           {nil, _}        -> 'cmd /c ' ++ command